1. Field of the Invention
The invention relates to optical modulators in general and particularly to an optical modulator that employs silicon (Si) as an active medium in a plasmonic device.
2. Description of Related Art
The integrated circuits ubiquitous in modern technology were critically enabled by the invention of the metal-oxide-semiconductor field effect transistor (MOSFET)—a three terminal device that modulates current flow between a source and drain via an applied electric field. Since the first successful demonstration of MOSFETs in the 1960's, silicon devices and circuits have continuously scaled according to Moore's law, increasing both the integration density and bandwidth of complementary metal-oxide-semiconductor (CMOS) networks. At present, microprocessors contain over 800 million transistors clocked at 3 GHz, with transistor gate lengths as small as 35 nm. Unfortunately, as gate lengths approach dimensions measured in single nanometers, MOS scaling is accompanied by increased circuit delay and higher electronic power dissipation. This is a substantial problem for Moore's Law which often referred to as the “interconnect bottleneck.”
To circumvent the electrical and thermal parasitics associated with MOS scaling, new interconnect technologies are being considered by various groups. Particular attention has been given to optical technologies, which could achieve high integration densities without significant electrical limitations. On-chip optical components would offer a substantially higher bandwidth, a lower latency, and a reduced power dissipation compared with electronic components. Unfortunately, optical components are generally bulky relative to CMOS electronic devices, comprising dimensions on the order of the signal wavelength.
The use of plasmonic components offers a unique opportunity for addressing the size mismatch between electrical and optical components. Plasmonic devices convert optical signals into surface electromagnetic waves propagating along metal-dielectric interfaces. Because surface plasmons exhibit extremely small wavelengths and high local field intensities, optical confinement can scale to deep subwavelength dimensions in plasmonic structures.
Recent reports have demonstrated passive and active plasmonic components that combine low optical loss with high mode confinement. Metal-dielectric channels and metal-insulator-metal slot structures have formed the basis for subwavelength plasmonic waveguides, interferometers, and resonators. In addition, plasmon modulators based on quantum dots, ferroelectric materials, or liquid crystals have been proposed and demonstrated. Unstrained silicon exhibits an indirect bandgap and no linear electro-optic effect, yielding a continuous-wave optical response that is typically either slow or weak. To date, neither a Si-based plasmonic waveguide nor a plasmonic Si-based modulator have been demonstrated.
There is a need for plasmonic devices having Si as the active medium in order to integrate standard Si-based electronics with Si-based photonics, and to allow for compatibility with standard CMOS processing techniques and the potential for integration into existing Si-based photonic networks.